1. Field of the Invention
The present invention relates to a method and an apparatus for scheduling in a mobile communication system, and more particularly to a method and an apparatus for allocating resources by an Evolved Node B according to a scheduling request transmitted in an uplink from a User Equipment (UE).
2. Description of the Related Art
A Universal Mobile Telecommunication Service (UMTS) system is a 3rd Generation (3G) asynchronous mobile communication system, which uses wideband Code Division Multiple Access (CDMA) and is based on Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS), which are used in European mobile communication systems. In the 3rd Generation Partnership Project (3GPP), which is in charge of standardization of the UMTS, active discussion is taking place about a Long Term Evolution (LTE) system as a next generation mobile communication system. The LTE technology is targeting commercialization by the year 2010 and the realization of high speed packet-based communication at a speed of about 100 Mbps. To this end, being discussed are various schemes, which include a scheme of reducing the number of nodes located in communication paths by simplifying the structure of a network, and a scheme of approaching a wireless protocol to a wireless channel as close as possible.
FIG. 1 illustrates an example of a structure of an Evolved UMTS mobile communication system to which the present invention is applicable.
Referring to FIG. 1, an Evolved UMTS Radio Access Network (E-RAN) 110 has a simplified 2 node structure, which includes Evolved Node Bs (ENBs) 120, 122, 124, 126, and 128 and anchor nodes 130 and 132. A User Equipment (UE) 101 is connected to an Internet Protocol (IP) network 114 through the E-RAN 110. The ENBs 120 to 128 correspond to legacy Node Bs of the UMTS system and are connected to the UE 101 through a wireless channel.
Different from legacy Node Bs, the ENBs 120 to 128 perform more complicated functions. In the LTE, all user traffic including the real-time service, such as Voice over IP (VoIP) using the Internet Protocol, is provided through a shared channel. Therefore, the LTE requires an apparatus for collecting status information of UEs and performing scheduling by using the collected information. The ENBs 120 to 128 take charge of the scheduling. Usually, one ENB controls a plurality of cells.
Further, the ENB performs Adaptive Modulation and Coding (AMC), which determines a modulation scheme and a channel coding rate in accordance with the channel status of a UE. As in High Speed Uplink Packet Access (HSUPA), which is also called “Enhanced Dedicated Channel (E-DHC)”, and High Speed Downlink Packet Access (HSDPA) of the UMTS, Hybrid Automatic Repeat reQuest (HARQ) is performed between the ENBs 120 to 128 and the UE 101 in the LTE also. Because it is impossible by only the HARQ to satisfy requirements for various Qualities of Service (QoSs), an outer Automatic Repeat Request (ARQ) in a higher layer may be performed between the UE 101 and the ENBs 120 to 128.
The HARQ process refers to a process of soft-combining previously-received data with retransmitted data without discarding the previously-received data, thereby improving the ratio of success in the reception. The HARQ process is used in order to improve the transmission efficiency in high speed packet communication, such as High Speed Downlink Packet Access (HSDPA) and Enhanced Dedicated Channel (EDCH). In order to implement a maximum transmission speed of 100 Mbps, the LTE is expected to use Orthogonal Frequency Division Multiplexing (OFDM) in 20 MHz bandwidth as wireless connection technology.
FIG. 2 illustrates an example of a conventional process for transmission of data/message to an ENB through a scheduling request by a UE.
The scheduling request refers to a request for allocation of radio resources necessary for Buffer Status Report (BSR), which is transmitted by a UE when it is necessary to transmit the BSR to an ENB, for example, when the UE has received new data/message to be transmitted in an uplink from a higher layer, or when the UE has received data/message of a new size to be transmitted in an uplink from a higher layer despite that it had previously assigned resources for uplink data/message transmission from an ENB. Through the BSR, the UE notifies the ENB of detailed information on data/message size, etc. to be transmitted to the ENB. Based on information obtained from the BSR, the ENB allocates radio resources corresponding to the data/message to the UE.
Referring to FIG. 2, reference numerals 201, 203, 205, 207, and 209 denote Radio Frame Numbers (RFNs), and reference numerals 211, 213, 215, 217, and 219 denote radio resources allocated to the UE for transmission of the scheduling request. Although not shown in FIG. 2, the radio resources 211, 213, 215, 217, and 219 are promised in advance between the ENB and the UE through a higher layer message. Although the radio resources 211, 213, 215, 217, and 219 shown in FIG. 2 are radio resources of particular time and particular frequency, there is no limit in what the time and frequency of a radio resource which a channel transmitting the scheduling request will use.
When it is necessary to transmit a scheduling request for any of the allocated radio resources 211, 213, 215, 217, and 219, the UE signals it. If it is unnecessary to transmit the scheduling request, the UE either may not use the radio resources or may signal the absence of the scheduling request by using the radio resources. The following description is based on an assumption that the UE does not perform any signaling by using the radio resources when it is unnecessary to transmit the scheduling request. However, the present invention is not limited to this assumption.
At time point 221, when it is necessary to transmit a scheduling request due to some reason, for example, when the UE has received new data or message to be transmitted in an uplink from a higher layer, the UE signals the scheduling request by using a next radio resource 215 that the UE is allocated for scheduling request. Upon receiving the scheduling request 231, the ENB transmits a resource grant message 241 to the UE, thereby allocating a radio resource for transmission of a BSR of the UE. Upon receiving the resource grant message 241, the UE transmits a BSR 245 to the ENB by using the radio resource 243 according to radio resource information included in the resource grant message 241. The BSR may include a size of data/message to be transmitted by the UE, priority information of a Radio Bearer (RB) for transmitting the data/message, etc. Upon receiving the BSR 245, the ENB transmits a resource grant message 251 to the UE according to the information included in the BSR 245, thereby allocating a radio resource for transmission of the data/message. Upon receiving the resource grant message 251, the UE transmits data/message 255 by using the radio resource 253 according to radio resource information included in the resource grant message 251.
In the conventional process as described above, each of radio resources 211, 213, 217, and 219 for a scheduling request is not used if it is unnecessary to transmit the scheduling request at a corresponding time point.
As described above, in order to transmit data/message to an ENB, a UE must perform a process including: transmitting a scheduling request; receiving a resource grant message for transmission of a BSR; transmitting the BSR; receiving a resource grant message for transmission of data/message; and transmitting the data/message. This process results in a long time delay before the data/message is actually transmitted. Therefore, this scheduling process is not proper for transmission of data/message sensitive to the delay.